An Incel would say to a femcel "I'll date you" and the femcels would say no therefore proving the Incels point thats its voluntary celibacy.

I won't lie, they would kinda have a point with that.

I am not suggesting incels and femcels should date each other, that probably would be a bad idea, but some people who call themselves incel/femcel are just overly picky with unrealistic expectations of the kind of partner they can reasonably expect to draw the attention of. That is not involuntary, that is quite literally voluntary.